Internal wave activity and its role on mixing, nutrient supply and
phytoplankton community structure during spring and neap tides in the Ría
de Vigo (NW Iberian Peninsula)
Marina Villamaña1*, Beatriz Mouriño-Carballido1, Emilio Marañón1, Pedro Cermeño 2, Paloma
Chouciño1, José C.B. da Silva3, Patricio A. Díaz4, Bieito Fernández-Castro1, Miguel Gilcoto5,
Rocío Graña5, Mikel Latasa6, Jorge M. Magalhaes3, José Luis Otero-Ferrer1, Beatriz Reguera4,
Renate Scharek6.
1
Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, 36310, Vigo, Spain.
Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Passeig Maritim de la Barceloneta, 37-49, E08003, Barcelona, Spain.
3
Departamento de Geociências, Ambiente e Ordenamento do Território, Universidade do Porto, Rua do Campo Alegre 687,
4169-007, Porto, Portugal.
4
Centro Oceanográfico de Vigo, Instituto Español de Oceanografía (IEO), Subida a Radio Faro 50, 36390 Vigo, Spain.
5
Instituto de Investigacións Mariñas, Consejo Superior de Investigaciones Científicas, Eduardo Cabello 6, 36208 Vigo, Spain.
6
Centro Oceanográfico de Gijón, Instituto Español de Oceanografía (IEO), Avda. Príncipe de Asturias, 70 bis, 33212, Gijón,
Spain.
2
ABSTRACT
Despite the evidences of internal wave activity in the NW Iberia upwelling region, their action and role on nutrient
supply dynamics and phytoplankton community structure remain unexplored. By using a multidisciplinary
approach combining the analysis of Synthetic Aperture Radar (SAR) images and field observations collected in
the outer part of the Ría de Vigo (NW Iberian Peninsula), we characterized the internal wave activity during
spring and neap tides, their influence on mixing and nutrient supply dynamics, and their role on phytoplankton
size-structure and composition. SAR images acquired during the summer months of the 2008-2011 period,
revealed that internal waves were more energetic during spring than neap tides, and that the most energetic
packets occurred close to the 100 and 150 m isobaths. The intensive sampling carried out in summer 2013,
including continuous measurements of microstructure turbulence and sampling for inorganic nutrient
concentration and phytoplankton size-structure and composition, showed that turbulence and mixing levels were
higher during spring than neap tides. As a result of increased mixing levels, nitrate diffusive input into the
euphotic layer was approximately 4-fold higher (35±89 mmol m-2 d-1) during spring tides. This nitrate input could
represent an important fertilizing mechanism during spring tides and summer stratification periods to explain the
continuous dominance of large-sized phytoplankton during the upwelling favorable season.
INTRODUCTION
During spring-summer months (April to September) the
NW Iberia is characterized by intense and intermittent
upwelling pulses [1]. In addition, during the upwelling
season the surface layer is characterized by high thermal
stratification, which is favorable for internal wave activity
and propagation. Enhanced mixing associated with internal
waves dissipation increase vertical nutrient transport,
which supports horizontal and vertical gradients in
phytoplankton community structure with important
implications for fisheries and the export of particulate
organic carbon [2,3].
A multidisciplinary approach comprising the analysis of
SAR images and the intensive sampling of physical,
chemical and biological variables was carried out in the
outer part of the Ría de Vigo in summer 2013 with the
following goals: 1) to characterize the internal wave
activity, 2) to quantify mixing levels and nutrient supply
into the photic zone, and 3) to describe the size-structure
and composition of the phytoplankton community during
spring and neap tides.
MATERIAL AND METHODS
A selection of 20 SAR images (8 ERS1&2-SAR images
and 12 Envisat-ASAR in Precision Image mode) acquired
during the summer months from 2008 to 2011 on the shelf
off the Ría de Vigo, was used to calculate a proxy for the
energy of the internal wave packets (E*) for spring and
neap tides [4,5]. Two cruises were conducted on board the
R/V Mytilus in the outer part of the Ría de Vigo (42.174ºN,
8.890ºW) during spring (20-21 August 2013, CHAOS1)
and neap (27-28 August 2013, CHAOS2) tides (Figure 1).
Fig. 1. Map showing the position of the intensive
observations carried out on board the R/V Mytilus
(42.174ºN - 8.890ºW) in the outer part of the Ría de Vigo
in summer 2013.
An intensive sampling (yo-yo) of measurements of
microstructure turbulence by using a microstructure
profiler (MSS), was carried out covering two complete
semi-diurnal tidal cycles (ca. 25 hours). Water samples
were collected for the determination of inorganic nutrient
concentration and phytoplankton size-structure and
composition.
As a consequence, the averaged nitrate diffusive flux
computed during spring tides (35±89 mmol m-2 d-1) was
almost four times higher than during neap tides (9±12
mmol m-2 d-1). Although microphytoplankton (>20 m)
cells dominated the phytoplankton community in both
cruises, the species composition was significantly different.
In CHAOS1, when the water column was stratified, smallsized diatoms such as Chaetoceros socialis and small-sized
Chaetoceros spp. were more abundant. These species were
replaced by larger ones (medium and large Chaetoceros
spp.) one week later when an intense upwelling pulse
occurred during CHAOS2.
Our results indicate that, especially during spring tides and
stratification conditions, enhanced mixing driven by
internal waves could represent an important fertilizing
mechanism which could contribute to explain the
continuous dominance of large-sized phytoplankton during
the upwelling favorable season.
ACKNOWLEDGMENTS
Funding for this study was provided by the Spanish
Ministry of Science and Innovation under the research
project CTM2012-30680 to B. Mouriño-Carballido. M.
Villamaña thanks the Spanish Ministry of Education,
Culture and Sports for a FPU (FPU014/05385) grant.
RESULTS AND DISCUSSION
REFERENCES
The proxy for internal wave energy revealed that, during
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